1. Field of the Invention
The present invention relates to an intake duct for a vehicle, which supplies air into an engine.
2. Description of the Related Art
As shown in FIG. 7, in vehicles, the outside air taken through a vehicular intake duct DC is supplied into an engine EG, via an air cleaner AC (see Japanese Patent Application Laid-Open No. 2006-322434). This vehicular intake duct DC is made by injection molding or blow molding of a synthetic resin and has an air stream passage 20 defined therein. As shown in FIG. 8, the vehicular intake duct DC is provided with an inlet part 22 having an inlet port 24 and formed into a laterally elongated flat shape. An outlet part 26 having an outlet port 28 connected to the air cleaner AC is formed in a substantially rectangular shape. Further, the vehicular intake duct DC is bent at a midway portion between the inlet part 22 and the outlet part 26. The inlet part 22 of the vehicular intake duct DC is, as shown in FIG. 7, attached to the top face of a radiator support 16 by bolts BL. Also in this construction, the inlet port 24 of the duct DC is disposed to face a small space S which is between an engine hood 14 of an engine room 12 and the radiator support 16.
Recently, safety measures against contact of a vehicle with a pedestrian have been enhanced; as a result, it is designed so that at the time of collision of a vehicle against the pedestrian, the engine hood 14 deforms downward to some extent to absorb the impact. This requires the vehicular intake duct DC located directly under the engine hood 14 not to interfere with the deformation of the engine hood 14. In addition, the vehicular intake duct DC needs to absorb the impact transmitted via the engine hood 14 as well as permits the deformation of the engine hood 14.
As mentioned above, because the inlet part 22 of the vehicular intake duct DS is disposed in the small space S, the open end of the inlet part 22 is formed to be inclined rearward and upward from the lower part to secure the stroke needed at the time the engine hood 14 deforms. In other words, the inlet port 24 provided at the open end of the inlet part 22 is inclined to face obliquely upward. Generally, air has such a property as to flow into the open side of the inlet port 24 of the vehicular intake duct DC at an angle orthogonal to the open side. As seen from FIG. 7, therefore, after flowing obliquely downward through the inlet port 24, the air flows, as shown by curve dotted lines, horizontally along the inner surfaces of the wall portions constituting the air stream passage 20. Since the air taken through the inlet port 24 tends to flow along the incident line directed obliquely downward in the aforementioned manner, the air stream tends to come away from the inner surface of the upper wall portion and to be biased in the lower area of the air stream passage 20. When this occurs, the air counter-flows in the upper area R of the air stream passage 20 at the inlet part 22. As is apparent from the above, when the open side of the inlet port 24 is formed askew, biasing and counter flow of the air stream occur in the air stream passage 20 of the inlet part 22. Both of these would stand in the way of smooth ventilation and lower the air ventilating performance of the intake duct.